Project Summary: The cardiac thin filament is the essential regulator of cardiac contractility and relaxation at the molecular level. It is comprised of five discrete proteins: cTnC, cTnI, cTnT, actin and tropomyosin that have co-evolved to sustain efficient cardiac performance at rest, during exercise and, importantly, to respond to pathologic stressors. Mutations in genes encoding each of these proteins have been definitively linked to the development of a range of human genetic cardiomyopathies, including hypertrophic (HCM) and dilated (DCM) forms. Despite 25 years of study to define the direct link(s) between the biophysical insult and the resultant complex cardiomyopathy, many questions remain and significantly limit our ability to use genotype to prognosticate and inform patient management. Recent clinical studies based on genotyped cohorts have established that the earliest stages of pathogenic remodeling precedes the development of overt cardiac hypertrophy or dilatation. This seminal observation raises the possibility that early therapeutic intervention focusing on the earliest molecular ?triggers? may prove successful in slowing the natural history of these complex disorders. To test this hypothesis, the current application builds on our prior funding period where we developed an innovative integrated approach to probing thin filament-linked HCM and DCM that incorporates computation, biophysics and whole-heart physiology. We have identified two distinct, common pathogenic pathways to study. In Aim 1 we will delineate the dynamic role of the Tropomyosin overlap domain and the coupled allosteric regulation by the cardiac Troponin T N terminus on the differential cardiac remodeling that defines hypertrophic and dilated cardiomyopathies linked to known mutations in the flexible tropomyosin overlap. And in Aim 2 we will define the potential modulatory role of altered cTnC Ca2+ dissociation kinetics in the activation of CaMKII signaling as a nodal point in the pathogenesis of sarcomeric hypertrophic cardiomyopathy. The successful completion of these Aims will both reveal novel disease mechanisms and directly test the potential for altering the natural history of genetic HCM and DCM.